Control system



Nqv.'2,1943. Q L 2,333,432

CONTROL SYSTEM F i led Sept. '2 4, 1940 V Inventor:

Walter O. bum,

by fizz/14:76AM

His Atb orney Patented Nov. 2, 1943 CONTROL SYSTEM Walter 0.. Loan,

New York West Orange, N. 32, assignor to General Electric Company,

a corporation of Application September 24, 19%, Serial No. 358,125

4 Claims.

This invention relates to a control system, and although not limited thereto, it has particular application to a heating" control system for regulating the operation of a heating device, such as a furnace which employs a solid fuel feedingarrangement, such as a stokcr.

In regulating the fire of a furnace which em ploys a Stoker, or similar solid fuel feeding arrangement, it is necessary to provide an arrangement for maintaining the fire during extended times when the thermostat in the space to be heated is not calling for heat. Such hold-dire control arrangements ordinarily use a timer for periodically operating the stoker to keep the fire alive and are particularly necessary during those seasons of the year when the fire must be kept going but the temperature of the -furnace is quite erratic since at certain times of the day it is relatively warm outside. When employing such periodic timer hold-fire equipment it is desirable to so control the stoker that a. hld-fire period will be only temporary in case it should commence at the end of a period during' which the stoker has been running as the result or a call for heat by the thermostat in the space to be heated, thereby providing in effect a skip-cycle for the hold-fire control, otherwise the furnace as well as the space heated thereby may become too hot.

It is, therefore, an object of my invention to provide an improved control system for periodically providing minimum stolrer hold-fire periods and only when necessary to increase the combustion by extending these minimum holdfire periods for furnaces which are automatically fed with a solid fuel.

Another object of my invention is to provide an improved periodic stolzer hold-fire control system capable of accomplishing the equivalent of a skip cycle by providing periodically a stoker hold-fire period that is a predetermined minimum Whenever the stolrer tire is in good--condi-' tion at the time each hold-fire period occurs, but is capable of selectively extending any minimum hold-fire period as long as necessary to increase the StOkQi combustion to a predetermined minimum hold-fire condition, and in addition is capable of selectively continuing the stoker operation as long as necessary to increase the stoker combustion to the minimum holdire condition whenever the stoker has been started into operation by the room thermostat and the call for heat thereby has been satisfied.

Further objects and advantages of my invention will become apparent from the following deproportional thereto, is above operated switch is responsive scription referring the ac ins, and the features of terize my invention yvi ticularity in the claim a part of this specification.

In the singie figure oi? the c illustrated a control 5 my invention, in the tion of a coal stoker,

In the arrangement ing, have provided riodically providing stolrer, and a thermostat a predetermined tomb is u perature for extending; the periods when the errat nace becomes too low. cally operated switch which. or minimum closed periods open periods, Therefore, ela 1 the electric motor which operates a source of electric supply, may energized at predetermined regular intervals when the timing device or periodically aotu switch moves to a circuit closing position, The timing device need remain in ti position for only a sufiioient length of in e pick "up the relay and close a therefor. The timer may the to the open circuit position a or may not be held in closed s, the holding circuit depending one: the temperature of the furnace. the nost operated switch is provided hold cuit so that when the temperature, other suitable temperature inside tl be temporarily value indicating that the st condition, the holding circui relay -s be opened at the end of each :er holdfire period, thus allowing the its open position, in order stoker motor. However, in case nace temperature to which -the c ll minimum value indicating the fire in good condition, then the holding circuit for the relay will be maintained closed. the he" statically operated switch so as to extend the temporary hold-fire period until the stolzer condition indicating temperature reaches predetermined value.

Referring more particularly to the drawing, I have indicated diagrammatically a conventional stoker operating motor I which may be conthe fire

nectcd to any suitable source of supply II and 12 through the lines 13 and Il. In order to control the energization oi the motor it I provide a switch 15 in the line II. This switch may be biased to the open position as shown in any suitable manner, such as through the biasing action oi. the movable core l6 a relay indicated generally by the numeral 11. This relay is provided with a coil it which when suitably energized will force the core towards the contacts of the switch 15 so as to close the motor circuit. In order to energize the relay I! at periodic intervals of time, I provide a switch it which may be periodically operated in any suitable manner, as, for example, by a clock motor 20. The motor 20 has provided on its shaft 2| a suitable cam 22 which cooperates with a peg 23 on the movable arm of the switch IS. The camming surface of the cam 22 is provided with an indentation or valley 24 so that each time the cam 22 makes a complete revolution the peg 23 may enter the indentation 24 and allow the switch 9 to move to its closed position. Since the valley 24 is provided in a relatively small part of the cam surface 22, my periodically actuated switch will be closed for relatively short or minimum periods and open for relatively long periods. These periods may be proportioned to any suitable amounts so that the switch may be closed for example, for 15 seconds and open for 15 minutes. Any other suitable periods, of course, may be provided and also any other suitable timing arrangement may be employed for properly periodically opening and closing the switch l9. Suitable low voltage for energizing the coil i8 is provided through the step-down transformer 25. One side of the secondary of the transformer is connected to one side of the coil 18 through the conductor 26 and the other side of the coil is connected to the other side of the secondary of the transformer 25 through the conductor 21, switch [9, conductor 28. In order to provide a holding circuit for the coil [8 the circuit which includes the conductor 21 and the switch I! is shunted by a circuit including a switch 29, conductor 30, and a thermostatically operated switch 3| which is responsive to a suitable temperature, such as stack temperature. The switch 29 may be conveniently operated by the core l8 which also operates the switch It, so that both switches close at the same time.

It will be seen, therefore, that, if the tempera ture responsively operated switch 3i is in its closed position, when the timing device moves the switch I! to its open position, the relay ll will be maintained in its energized position through the circuit which includes the conductor 26, relay coil l8, conductor 10, switch 3|, and conductor 28.

The thermostat which is placed in the space to be heated is indicated by the numeral 32 and it will be seen that when this thermostat calls for heat it will close its contacts and complete the circuit which includes the conductor 26, the coil It, the conductor 21, and conductors 23, 34, and 28.

In order to prevent the hold-fire control or the room thermostat from starting the stoker motor if the fire has gone out, any suitable outfire control equipment may be provided. Thus, a thermostatically operated switch 35 may be provided in the line 28 between the switches 3| and i9 and one side of the transformer 25. The contacts of this thermostat 35 will be normally closed and will be designed to open at a low temperature, that is when the flre had gone out. When the out-fire control is provided, a reset mechanism may also be provided for by-passing the out-fire control during the starting of the fire. Thus, a normally open switch 30 may be shunted across the out-fire thermostatic switch 35; that is, it may be connected between the lines 34 and 28. The reset mechanism may be controlled in any suitable manner, such as the operator manually holding the reset switch closed to operate the stoker motor Ill during the starting of the stoker fire in the furnace, and when the fire has sufficiently increased so as to close the out-fire switch, the reset mechanism may be allowed to move to its open position under its own bias. Also, any suitable automatically operated device, such as a timer, may be employed for controlling the reset mechanism.

The operation of my improved hold-fire control system is as follows: The hold-fire period is initiated by the closing 01' the periodically actuated switch It. This circuit may be traced from one side of the transformer 25 through the conductor 28, relay coil l8, conductor 21, switch i9, switch 35, conductor 28, back to the other side of the secondary oi the transformer 25. This energization of the relay coil l8 will caus the switch l5 to move to its closed position so that the motor ID will be connected to the source of supply and therefore operate to increase the stoker combustion. At the same time the switch 28 will close in order to provide a holding circuit for the coil It. This holding coil circuit includes the conductor 28, coil l8, switch 29, conductor 80, thermostatically operated switch 3 I, switch 35, and conductor 28. Thus, at the end of a relatively short or minimum period of time the switch I! will move to its open circuited position, but the relay I1 will be maintained in its energized position, if the contacts of the thermostat 3| are in their closed position. The thermostat 3| may be responsive to the furnace temperature or the stack temperature, or any other suitable temperature dependent upon the condition of the stoker fire, and it may be made to open its contacts at any suitable predetermined minimum temperature, such as 350 degrees F. when it is responsive to stack temperature.

Since the holding circuit for the relay coil It includes a thermostatically operated switch responsive to stack temperature the hold-fire period will be maintained for only so long a time necessary to bring the fire up to a suitable point so that the stack temperature is raised to a sufficient predetermined minimum value. Thus, the hold-fire circuit will be provided so that a minimum of fuel will be used, and the equivalent of a so called skip-cycle for the hold-fire period will be provided whenever the periodically actuated twitch l8 moves to its closed position just following the period when the stoker has been run to satisfy a call for heat by the room thermostat 32 or whenever the stack temperature is above a predetermined minimum value. Therefore, by providing a hold-fire control circuit which is initiated at predetermined intervals of time, but the length or the hold-fire period being controlled thermostatically, I-provide a system which will maintain the furnace temperature at a desired value but which will not allow this value to raise above a predetermined value during the holdl'ire period.

It will be seen therefore, from the above, that I have provided a control system which includes a reiay,-the energization of which is initiated by accuses a suitable timing device and the length oi time in its energized position is controlled by a thermostatically actuated switch. Such a circuit may be advantageously employed in a heating control circuit for controlling the hold-fire period for a fuel feeding device for a furnace.

Modifications oi the particular arrangement which I have disclosed embodying my invention will occur to those skilled in the art, so that I do not desire my invention to be limited to the particular arrangement set forth and I intend in the appended claims to cover all modifications which do not depart from the spirit and scope of my invention. 1

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a hold-fire control system for a stoker having a motor operable to increase the stoker combustion, a switch for controlling operation of said motor, means including a coil for operating said switch to operate said motor, an energizing circuit for said coll, a thermostat for closing said circuit to operate said motor, a holding circuit for said coil, means including a continuously operating timer for temporarily closing said energizing circuit at regular intervals to provide periodic short hold-fire operating periods for said motor irrespective of said thermostat operation, and a second thermostat responsive to a. temperature dependent on the stoker combustion for closing said holding circuit to continue operation of said motor upon the opening of said energizing circuit by said timer and said first thermostat as long as said temperature is below a predetermined minimum hold-fire value.

2'. A stoker control system including a relay for controlling operation of the stoker and having an operating coil and at least four switches for'controlling the energmation of said coil, two of said switches being connected in parallel in an energizing circuit for separately energizing said coil, and the other two of said switches being connected in series in a holding circuit for main-- taining said coil energized, thermostatic means for operating one of said first two switches, means including a continuously operating timer having relatively short on periods and relatively long on? periods for periodically operating the other oi said first two switches to periodically provide minimum stoker hold flre energizing periods for said relay, means effective upon energiaation oi said coil for closing one of said second two switches, and a thermostat responsive to a temperature dependent on the-Stoker combustion for closing the other of said second two switches to complete said holding circuit and extend said minimum stolrer hold-fire energizing periods of said relay only when. said temperature is below a predetermined "minimum hold-fire value.

d. in a hold-fire control for a stoker having a motor operated fuel feed device, an energizing relay for said motor having an energizing circuit and holding circuit, a continuously operating timer having a switch connected in said energizins circuit and closed for relatively short periods and opened for relatively long periods for periodically energinngsaid motor to provide temporary hold-fire periods at regular intervals, and means for extending said temporary hold-fire periods including a thermostatic switch responsive to a temperature dependent upon combustion of the fuel and a switch operated by said relay upon energization thereof for jointly completing. said holding circuit only when said temperature is below a predetermined value. I

i. In a hold-fire control system for astoker having a motor driven fuel feeding device, a motor energizing relay having an energizing circuit and a holding circuit, a room thermostat and a parallel connected, continuously operating periodic time switch separately controlling said energizing circuit, said time switch having relativeiy short circuit closing periods and relatively long circuit opening periods, and a thermostatic switch responsive to a temperature dependent upon the iuel combustion for closing said holding circuit to maintain said relay energized only when said temperature is below a. predetermined .value upon the opening of said energizing circuit by both said room thermostat and said time switch.

WALTER O. LUM. 

